In a resource-limited situation, when bone flaps placed in the abdomen undergo demineralisation and sutures are used to fix the flap as opposed to plates, where artificial cranial flap substitutes are prohibitively expensive and frequent postoperative imaging may not be feasible, prevention and management of this complication will continue to remain a problem 2).
Aseptic bone resorption or aseptic bone necrosis of reimplanted autologous bone flaps occurred more frequently in the series of patients than in most reports in the literature. Most cases were identified between 6 and 12 months postoperatively. Clinical observation or CT scans of patients with autologous bone flaps are recommended for at least 12 months. Patient-specific implants may be preferable to autologous bone flaps 3).
Bone flaps removed during decompressive craniectomy are commonly frozen at -80 °C and stored until cranioplasty. Histological integrity and regenerative capacity have been shown for cryoconserved bone. The effects of cryoconservation on the surface structure are unknown, although these might cause mechanical instability or facilitate bacterial adhesion. This study evaluates the surface structure of cryoconserved bone by scanning electron microscopy. Five patients were identified who could not receive their autologous bone flaps after decompressive craniectomy. These redundant bone specimens were obtained after cryoconservation for 6-8 months and the outer surface was analyzed by scanning electron microscopy. We found varying surface structures which did not correlate with any variables, such as patient age, gender or duration of freezing, and probably reflect physiological interindividual variation. Pathological findings, such as microscopic crack formation, were not observed. Cryoconservation for up to 8 months does not appear to alter the surface structure of skull bone on scanning electronic microscopy 5).
Schwarz et al. retrospectively analyzed 631 cranioplasty procedures (503 with autograft, 128 with bone substitute) by using a stepwise multivariable logistic regression model and discriminant function analysis.
There was a significantly higher risk for reoperation after placement of autograft than after placement of bone substitute; aseptic bone necrosis (n = 108) was the major problem (OR 2.48 [95% CI1.11-5.51]). Fragmentation of the flap into 2 or more fragments, younger age (OR 0.97 [95% CI 0.95-0.98]; p < 0.001), and shunt-dependent hydrocephalus (OR 1.73 [95% CI1.02-2.92]; p = 0.04) were independent risk factors for bone necrosis. According to discrimination analysis, patients younger than 30 years old and older patients with a fragmented flap had the highest risk of developing bone necrosis.
Development of bone flap necrosis is the main concern in long-term follow-up after cranioplasty with autograft. Patients younger than 30 years old and older patients with a fragmented flap may be candidates for an initial artificial bone substitute rather than autograft 6).